Conventionally, there have been proposed stent delivery systems for putting a stent indwelling in a stenosed part or occluded part in a living body lumen or a body cavity such as a blood vessel, a bile duct, an esophagus, a trachea, an urethra, a digestive tract or the like organ so as to secure or maintain a lumen or body cavity space.
The stents delivered by the above-mentioned stent delivery systems are classified, by the function or the method of putting the stent indwelling, into balloon-expandable stents and self-expanding stents.
The balloon-expandable stent is a stent which itself does not have an expanding function. In order to put such a stent indwelling in a target part, for example, the stent mounted on a balloon is inserted into the target part, and thereafter expansion (plastic deformation) of the stent is effected by a dilating force of the balloon, whereby the stent is put into close contact with an inner surface of the target part and fixed in situ.
This type of stent requires a stent-expanding operation as discussed above, but it has little difficulty being put in an indwelling state, because the stent can be mounted directly on the contracted balloon and put indwelling in the target part.
On the other hand, the self-expanding stent is a stent which itself has contracting and expanding functions. In order to put this stent indwelling in a target part, the stent in the contracted state is inserted into the target part, and thereafter the stress loaded for maintaining the contracted state is removed. For instance, the stent is contained in its contracted state in a sheath having an outside diameter smaller than the inside diameter of the target part, the distal end of the sheath is brought to the target part, and thereafter the stent is pushed out of the sheath. The stent thus pushed out is released from the sheath, whereby the stress applied to the stent is removed, so that the stent expands and is restored to its shape before contraction. As a result, the stent is put in close contact with the inner surface of the target part and fixed in situ.
This type of stent is a stent which itself has an expanding force, and, therefore, does not need a stent-expanding operation, unlike balloon-expandable stents. This type of stent does not suffer from the difficulty that a reduction in diameter is induced by the pressure of a blood vessel or the like, leading to restenosis.
However, self-expanding stents are generally said to be more difficult to accurately put indwelling, than balloon-expandable stents. The reason is as follows. In the case of a balloon-expandable stent, after the stent is placed in a target stenosis part, it is necessary to inject a liquid into the balloon to expand and position the stent. Therefore, the stent does not move distally or proximally at the time of expansion. On the other hand, a delivery system for a self-expanding stent is constructed so that the stent is restrained by containing it between an inner tube and an outer tube, a lock section for restricting movement of the stent is provided on the stent proximal side of the inner tube, and the outer tube is pulled toward the proximal side, whereby the stent is released from being restrained and is permitted to self-expand. In this case, the stent is said to be liable to move distally at the time of expansion, due to loosening of the outer tube in a body cavity, friction between the outer tube and the body cavity or a catheter in which the outer tube is introduced, or friction between the outer tube and a valve of a device called introducer for introducing the system into a living body.
In view of the foregoing, the present applicant proposed a system shown in Japanese Application Publication No. 2007-97620 which corresponds to U.S. Application Publication No. 2006/0259124.
This stent delivery system 1 includes a distal-side tube 2 having a guide wire lumen 21, a proximal-side tube 4 fixed to a proximal section of the distal-side tube 2, a stent-containing tubular member 5 which envelops the distal side of the distal-side tube 2 and which is slidable in the proximal direction, a stent 3 contained in the tubular member 5, and a wire 6 for moving the tubular member 5 toward the proximal side. The distal-side tube 2 has a proximal-side opening 23 opening on the proximal side of the distal-side tube 2, a stent lock section 22 for restricting movement of the stent toward the proximal side, and an operating section equipped with a wire winding mechanism and a wire winding amount restriction mechanism. This stent delivery system has a merit in that it is free of generation of needless curving or damage of a catheter due to excessive winding of the wire for pulling toward the proximal side the tubular member 5 serving as a restraint body for the stent.
The system disclosed in the above-cited application publication is sufficiently effective in that the wire winding mechanism is composed of an operating rotary roller, and a winding shaft section rotated by the rotation of the roller. In addition, the wire winding amount restriction mechanism is composed of a winding restricting linear body of a predetermined length and having one end gripped by an operating section, and the other end fixed to a winding shaft section of the operating rotary roller or to a linear body winding shaft section provided separately from the winding shaft section. By rotating the operating rotary roller in a wire winding direction, the linear body is wound onto the linear body winding shaft section by a predetermined amount, whereon further winding is impossible. In this stent delivery system, however, both the wire and the winding restricting linear body are wound by the rotation of the operating rotary roller, so that rotational resistance on the operating rotary roller cannot be lowered. In addition, the above-mentioned application publication discloses an embodiment wherein the wire winding amount restriction mechanism is composed of a projected section provided on the operating rotary roller, and a lock section which is provided inside the operating section and makes contact with the operating rotary roller, after rotation of the operating rotary roller by a predetermined amount in a wire winding direction, so as to restrict further rotation of the operating rotary roller. In the system according to this embodiment, however, the operating rotary roller can be set only to a rotating amount of less than one revolution, so that the wire winding amount which can be restricted by the wire winding amount restriction mechanism is small.